(111) oriented (GaAs)n(AlAs)n superlattices are direct band-gap materials for all n’s

Abstract

Total energy calculations show that the (111) (AlAs)n(GaAs)n superlattice has a lower formation enthalpy (i.e., is stabler) than either the (001) or (110) superlattices. Self-consistent band structure calculations further show that while the (001) superlattice is direct only for n>7, the (111) superlattice has (i) a smaller and (ii) a direct (not pseudodirect) gap for all n’s. Contrary to the expectations based on particle in a box models, the confined states at the zone center are strongly localized even for the monolayer superlattice.